1. Field of the Invention
This invention relates to an electron spin resonator, and more particularly to an electron spin resonator provided with means for detecting resonance signals by sweeping a frequency.
2. Description of the Related Art
Conventionally, most electron spin resonators employ a system for sweeping a magnetic field for a signal detection. In the electron spin resonator of the magnetic field sweeping system, a sample placed in a static magnetic field is applied with a micro-wave magnetic field and further the static magnetic field is so swept as to capture an absorption of an energy of the micro-wave into the sample with an electron spin resonance. Normally, the sweep of the static magnetic field is accomplished by sweeping an excitation current of a permanent magnet which generates a static magnetic field. A large power PG,3 source for the excitation and a cooling to compensate for a heat generation from a sweep coil are necessary. There is an electron spin resonator employing a system for sweeping a frequency by use of permanent magnets without any large excitation power source. A range of the sweep is limited into an extremely narrow band.
In the above mentioned electron spin resonator, the magnetic field sweeping system becomes the main current rather than the frequency sweeping system because the frequency sweeping system primary has the following two problems. The first problem is a difficulty in a wide range sweep of the micro-wave frequency. The second problem is that a quality factor Q of micro-wave cavity resonators is very high thereby it is possible to response a frequency in a very narrow range only.
The former problem will be described in detail. For tuning a frequency of a micro-wave oscillator, a mechanical tuning and an electrical tuning are generally used together with one another. In a measurement of the electron spin resonance, the electrical tuning of the oscillator is employed to accomplish a smooth and continuous sweep. It seems that a sweep range of approximately 10% is necessary for the measurement of the electron spin resonance ordinary used. In klystrons widely and conventionally used, a variable range of a frequency against an output frequency for the mechanical tuning is 5% to 10%, but that for the electrical tuning is only 0.2% to 0.5%. Even when a varactor is used together with a gunn diode recently and widely used, it is approximately 0.5%. The electric tuning was therefore unable to accomplish a wide range sweep of the frequency of the micro-wave.
With respect to the latter, a quality factor Q of the cavity resonator for detecting the electron spin resonance signals is high, or 4,000 to 10,000. The resonant frequency is determined almost by a mechanical size of the resonator. Then, it is impossible to accomplish a wide range sweep of the frequency.
However, if the problems are solved, a change from the magnetic field sweep system into the frequency sweep system is able to make it unnecessary to use the large power source for the excitation and a cooling water and the like. Such change is further able to make the electron spin resonator free from an institutional facility accommodating a power source and a water supply equipment so that the electron spin resonator becomes portable for a considerable reduction of conditions of the measurement and the facility thereof.